COUNT() : Get count of records

COUNT() function returns the number of rows that matches a specified criteria.

I am going to use following sample data.

CREATE TABLE employee(

  id int PRIMARY KEY,

  name VARCHAR(25),

  age int,

  salary DECIMAL(10, 4),

  mailId VARCHAR(25),

  city VARCHAR(10)

);

INSERT INTO employee VALUES (1, "Hari", 28, 12345.67, "hari@hari.com", "Bangalore");

INSERT INTO employee VALUES (2, "Sandesh", 31, 98345.00, "sandesh@sandesh.com", "Trivendram");

INSERT INTO employee VALUES (3, "Phalgum", 33, 119345.67, "phalgun@hari.com", "Hyderabad");

INSERT INTO employee VALUES (4, "Manju", 36, 87666.87, "manju@sandesh.com", "Bangalore");

INSERT INTO employee VALUES (5, "Rakesh", 26, 38000, "rakesh@hari.com", "Bangalore");

INSERT INTO employee VALUES (6, "Sankalp", 38, 87645.67, "sankalp@sankalp.com", "Chenai");

INSERT INTO employee VALUES (7, "Vadiraj", 40, 12345.67, "vadi@hari.com", "Bangalore");

INSERT INTO employee VALUES (8, "Prasob", 37, 12345.67, "prasob@sandesh.com", "Trivendram");

INSERT INTO employee (id, name, salary) VALUES (9, "Kesav", 123457.89);

mysql> SELECT * FROM employee;
+----+---------+------+-------------+---------------------+------------+
| id | name    | age  | salary      | mailId              | city       |
+----+---------+------+-------------+---------------------+------------+
|  1 | Hari    |   28 |  12345.6700 | hari@hari.com       | Bangalore  |
|  2 | Sandesh |   31 |  98345.0000 | sandesh@sandesh.com | Trivendram |
|  3 | Phalgum |   33 | 119345.6700 | phalgun@hari.com    | Hyderabad  |
|  4 | Manju   |   36 |  87666.8700 | manju@sandesh.com   | Bangalore  |
|  5 | Rakesh  |   26 |  38000.0000 | rakesh@hari.com     | Bangalore  |
|  6 | Sankalp |   38 |  87645.6700 | sankalp@sankalp.com | Chenai     |
|  7 | Vadiraj |   40 |  12345.6700 | vadi@hari.com       | Bangalore  |
|  8 | Prasob  |   37 |  12345.6700 | prasob@sandesh.com  | Trivendram |
|  9 | Kesav   | NULL | 123457.8900 | NULL                | NULL       |
+----+---------+------+-------------+---------------------+------------+
9 rows in set (0.00 sec)

Count number of employees in employee table.

mysql> SELECT COUNT(*) FROM employee;
+----------+
| COUNT(*) |
+----------+
|        9 |
+----------+
1 row in set (0.00 sec)

Count number of employees staying in Bangalore

mysql> SELECT COUNT(*) FROM employee WHERE city="Bangalore";
+----------+
| COUNT(*) |
+----------+
|        4 |
+----------+
1 row in set (0.00 sec)

Display city and count of employees

mysql> SELECT city, COUNT(*) FROM employee GROUP BY city;
+------------+----------+
| city       | COUNT(*) |
+------------+----------+
| NULL       |        1 |
| Bangalore  |        4 |
| Chenai     |        1 |
| Hyderabad  |        1 |
| Trivendram |        2 |
+------------+----------+
5 rows in set (0.00 sec)

As you see it display the NULL values also, you can escape NULL values using following query.

mysql> SELECT city, COUNT(*) FROM employee WHERE CITY IS NOT NULL GROUP BY city; 
+------------+----------+
| city       | COUNT(*) |
+------------+----------+
| Bangalore  |        4 |
| Chenai     |        1 |
| Hyderabad  |        1 |
| Trivendram |        2 |
+------------+----------+
4 rows in set (0.00 sec)

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